Forming instruction groups based on decode time instruction optimization

ABSTRACT

Instructions are grouped into instruction groups based on optimizations that may be performed. An instruction is obtained, and a determination is made as to whether the instruction is to be included in a current instruction group or another instruction group. This determination is made based on whether the instruction is a candidate for optimization, such as decode time instruction optimization. If it is determined that the instruction is to be included in another group, then the other group is formed to include the instruction.

BACKGROUND

One or more aspects relate, in general, to processing within aprocessing environment, and in particular, to optimizing the processing.

Processors execute instructions that direct the processors to performspecific operations. The instructions may be part of user applicationsthat perform user-defined tasks, or part of operating systemapplications that perform system level services, as examples.

One processing technique used by the processors to process theinstructions is referred to as pipelined processing, in which processingis performed in stages. Example stages include a fetch stage in whichthe processor fetches an instruction from memory; a decode stage inwhich the fetched instruction is decoded; an execute stage in which thedecoded instruction is executed; and a complete stage in which executionof the instruction is completed, including updating architectural staterelating to the processing. Other and/or different stages are possible.

To facilitate processing within a pipelined processor, variousoptimization techniques are employed. One such technique includes decodetime instruction optimization, which offers an opportunity to improvecode execution by combining multiple instructions into a single internalinstruction; recombining multiple instructions into multiple/fewerinternal instructions; and/or recombining multiple instructions intomultiple internal instructions with fewer data dependencies.

BRIEF SUMMARY

Shortcomings of the prior art are overcome and additional advantages areprovided through the provision of a computer program product forfacilitating processing within a processing environment. The computerprogram product includes a computer readable storage medium readable bya processing circuit and storing instructions for execution by theprocessing circuit for performing a method. The method includes, forinstance, obtaining an instruction to be executed in the processingenvironment; determining whether the instruction is to be included in acurrent group of instructions or a new group of instructions, whereinthe determining is based on whether the instruction is a candidate foroptimization with another instruction according to an optimizationcriterion; based on determining the instruction is to be included in thenew group of instructions, forming the new group of instructions, thenew group of instructions including the instruction and the anotherinstruction; and based on forming the new group of instructions,executing at least one instruction associated with the new group ofinstructions.

Methods and systems relating to one or more aspects are also describedand claimed herein. Further, services relating to one or more aspectsare also described and may be claimed herein.

Additional features and advantages are realized through the techniquesdescribed herein. Other embodiments and aspects are described in detailherein and are considered a part of the claimed aspects.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects are particularly pointed out and distinctly claimedas examples in the claims at the conclusion of the specification. Theforegoing and objects, features, and advantages of one or more aspectsare apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 depicts one embodiment of a processing environment to incorporateand use one or more aspects of a grouping capability to groupinstructions;

FIG. 2 depicts further details of a processor of the processingenvironment of FIG. 1;

FIG. 3 depicts one embodiment of an instruction pipeline of a processorof a processing environment;

FIG. 4A depicts one embodiment of decoders used to decode instructionsand provide optimizations;

FIG. 4B depicts one example of an optimization provided by a decoder;

FIG. 4C depicts another example of an optimization provided by adecoder;

FIGS. 5A-5B depicts examples of group formation;

FIG. 6A depicts one embodiment of logic to form an instruction group;

FIG. 6B depicts another embodiment of logic to form an instructiongroup;

FIG. 6C depicts yet another embodiment of logic to form an instructiongroup;

FIG. 7A depicts one embodiment of logic used to mark instructions, inwhich the markings are used to group instructions;

FIG. 7B depicts one embodiment of logic to form an instruction groupbased on the markings of FIG. 7A;

FIGS. 8A-8B depict examples of group formation;

FIG. 9 depicts another embodiment of logic to form an instruction group;

FIG. 10A depicts another embodiment of logic used to mark instructions;

FIG. 10B depicts one embodiment of forming an instruction group based onthe marking of FIG. 10A;

FIG. 11 depicts one example of a decode logic used to form groups ofinstructions and/or optimize groups of instructions;

FIG. 12 depicts one embodiment of a computer program product;

FIG. 13 depicts one embodiment of a host computer system;

FIG. 14 depicts a further example of a computer system;

FIG. 15 depicts another example of a computer system comprising acomputer network;

FIG. 16 depicts one embodiment of various elements of a computer system;

FIG. 17A depicts one embodiment of the execution unit of the computersystem of FIG. 16;

FIG. 17B depicts one embodiment of the branch unit of the computersystem of FIG. 16;

FIG. 17C depicts one embodiment of the load/store unit of the computersystem of FIG. 16; and

FIG. 18 depicts one embodiment of an emulated host computer system toincorporate and use one or more aspects.

DETAILED DESCRIPTION

In accordance with one or more aspects, a grouping capability isprovided that groups instructions into instruction groups based onoptimizations that may be performed. The groups are formed, forinstance, at decode or pre-decode time (both of which are referred toherein as decode time), and therefore, they are also referred to asdecode groups. The decode groups are formed, in one aspect, based ondecode time instruction optimizations that may be performed.

This grouping capability may be used in many different processingenvironments executing different processors. For instance, it may beused with processors based on the z/Architecture offered byInternational Business Machines Corporation. One or more of theprocessors may be part of a server, such as the System z server, whichimplements the z/Architecture and is offered by International BusinessMachines Corporation. One embodiment of the z/Architecture is describedin an IBM publication entitled, “z/Architecture Principles ofOperation,” IBM Publication No. SA22-7832-09, Tenth Edition, September2012, which is hereby incorporated herein by reference in its entirety.In one example, one or more of the processors executes an operatingsystem, such as the z/OS operating system, also offered by InternationalBusiness Machines Corporation. IBM, Z/ARCHITECTURE and Z/OS areregistered trademarks of International Business Machines Corporation,Armonk, N.Y., USA. Other names used herein may be registered trademarks,trademarks, or product names of International Business MachinesCorporation or other companies.

In a further embodiment, the processors are based on the PowerArchitecture offered by International Business Machines Corporation, andmay be, for instance, Power 700 series processors. One embodiment of thePower Architecture is described in “Power ISA Version 2.07,”International Business Machines Corporation, May 3, 2013, which ishereby incorporated herein by reference in its entirety. POWERARCHITECTURE is a registered trademark of International BusinessMachines Corporation.

One particular example of a processing environment to incorporate anduse one or more aspects of the grouping capability is described withreference to FIG. 1. In this particular example, the processingenvironment is based on the Power Architecture offered by InternationalBusiness Machines Corporation, but this is only one example. One or moreaspects are applicable to other architectures offered by InternationalBusiness Machines Corporation or other companies.

Referring to FIG. 1, a processing environment 100 includes, forinstance, a central processing unit (CPU) 110, which is coupled tovarious other components by an interconnect 112, including, for example,a read-only memory (ROM) 116 that includes a basic input/output system(BIOS) that controls certain basic functions of the processingenvironment, a random access memory (RAM) 114, an I/O adapter 118, and acommunications adapter 120. I/O adapter 118 may be a small computersystem interface (SCSI) adapter that communicates with a storage device121. Communications adapter 120 interfaces interconnect 112 with anetwork 122, which enables processing environment 100 to communicatewith other systems, such as remote computer 124.

Interconnect 112 also has input/output devices connected thereto via auser interface adapter 126 and a display adapter 136. Keyboard 128,trackball 130, mouse 132 and speaker 134 are all interconnected to bus112 via user interface adapter 126. Display 138 is connected to systembus 112 by display adapter 136. In this manner, processing environment100 receives input, for example, through keyboard 128, trackball 130,and/or mouse 132, and provides output, for example, via network 122, onstorage device 121, speaker 134 and/or display 138, as examples. Thehardware elements depicted in processing environment 100 are notintended to be exhaustive, but rather represent example components of aprocessing environment in one embodiment.

Operation of processing environment 100 can be controlled by programcode, such as firmware and/or software, which typically includes, forexample, an operating system such as AIX® (AIX is a trademark ofInternational Business Machines Corporation) and one or more applicationor middleware programs. As used herein, firmware includes, e.g., themicrocode, millicode and/or macrocode of the processor. It includes, forinstance, the hardware-level instructions and/or data structures used inimplementation of higher level machine code. In one embodiment, itincludes, for instance, proprietary code that is typically delivered asmicrocode that includes trusted software or microcode specific to theunderlying hardware and controls operating system access to the systemhardware. Such program code comprises instructions discussed below withreference to FIG. 2.

Referring to FIG. 2, further details of a processor 200 (e.g., centralprocessing unit 110) of the processing environment are discussed. In oneexample, the processor is a super-scalar processor, which retrievesinstructions from memory (e.g., RAM 114 of FIG. 1) and loads them intoinstruction sequencing logic (ISL) 204 of the processor. The instructionsequencing logic includes, for instance, a Level 1 Instruction cache (L1I-cache) 206, a fetch-decode unit 208, an instruction queue 210 and adispatch unit 212. In one example, the instructions are loaded in L1I-cache 206 of ISL 204, and they are retained in L1 I-cache 206 untilthey are required, or replaced if they are not needed. Instructions areretrieved from L1 I-cache 206 and, in one embodiment, are grouped intoinstruction groups and decoded by fetch-decode unit 208. After decodinga current instruction, the current instruction is loaded intoinstruction queue 210. Dispatch unit 212 dispatches instructions frominstruction queue 210 into register management unit 214, as well ascompletion unit 221. Completion unit 221 is coupled to general executionunit 224 and register management unit 214, and monitors when an issuedinstruction has completed.

When dispatch unit 212 dispatches a current instruction, unified mainmapper 218 of register management unit 214 allocates and maps adestination logical register number to a physical register withinphysical register files 232 a-232 n that is not currently assigned to alogical register. The destination is said to be renamed to thedesignated physical register among physical register files 232 a-232 n.Unified main mapper 218 removes the assigned physical register from alist 219 of free physical registers stored within unified main mapper218. Subsequent references to that destination logical register willpoint to the same physical register until fetch-decode unit 208 decodesanother instruction that writes to the same logical register. Then,unified main mapper 218 renames the logical register to a differentphysical location selected from free list 219, and the mapper is updatedto enter the new logical-to-physical register mapper data. When thelogical-to-physical register mapper data is no longer needed, thephysical registers of old mappings are returned to free list 219. Iffree physical register list 219 does not have enough physical registers,dispatch unit 212 suspends instruction dispatch until the neededphysical registers become available.

After the register management unit 214 has mapped the currentinstruction, issue queue 222 issues the current instruction to generalexecution engine 224, which includes execution units (EUs) 230 a-230 n.Execution units 230 a-230 n are of various types, including, forinstance, floating-point (FP), fixed-point (FX), and load/store (LS).General execution engine 224 exchanges data with data memory (e.g., RAM114, ROM 116 of FIG. 1) via a data cache 234. Moreover, issue queue 222may contain instructions of floating point type or fixed-point type,and/or load/store instructions. However, it should be appreciated thatany number and types of instructions can be used. During execution, EUs230 a-230 n obtain the source operand values from physical locations inregister files 232 a-232 n and store result data, if any, in registerfiles 232 a-232 n and/or data cache 234.

Register management unit 214 includes, for instance: (i) mapper cluster215, which includes architected register mapper 216, unified main mapper218, and intermediate register mapper 220; and (ii) issue queue 222.Mapper cluster 215 tracks the physical registers assigned to the logicalregisters of various instructions. In one embodiment, architectedregister mapper 216 has 16 logical (i.e., not physically mapped)registers of each type that store the last, valid (i.e., checkpointed)state of logical-to-physical register mapper data. However, it should berecognized that different processor architectures can have more or lesslogical registers than described in this embodiment. Further,architected register mapper 216 includes a pointer list that identifiesa physical register which describes the checkpointed state. Physicalregister files 232 a-232 n typically contain more registers than thenumber of entries in architected register mapper 216. It should be notedthat the particular number of physical and logical registers that areused in a renaming mapping scheme can vary.

In contrast, unified main mapper 218 is typically larger (typicallycontains up to 20 entries) than architected register mapper 216. Unifiedmain mapper 218 facilitates tracking of the transient state oflogical-to-physical register mappings. The term “transient” refers tothe fact that unified main mapper 218 keeps track of tentativelogical-to-physical register mapping data as the instructions areexecuted out-of-order (OoO). Out-of-order execution typically occurswhen there are older instructions which would take longer (i.e., makeuse of more clock cycles) to execute than newer instructions in thepipeline. However, should an out-of-order instruction's executed resultrequire that it be flushed for a particular reason (e.g., a branchmiss-prediction), the processor can revert to the checkpointed statemaintained by architected register mapper 216 and resume execution fromthe last, valid state.

Unified main mapper 218 makes the association between physical registersin physical register files 232 a-232 n and architected register mapper216. The qualifying term “unified” refers to the fact that unified mainmapper 218 obviates the complexity of custom-designing a dedicatedmapper for each of register files 232 (e.g., general-purpose registers(GPRs), floating-point registers (FPRs), fixed-point registers (FXPs),exception registers (XERs), condition registers (CRs), etc.).

In addition to creating a transient, logical-to-physical register mapperentry of an out-of-order instruction, unified main mapper 218 also keepstrack of dependency data (i.e., instructions that are dependent upon thefinishing of an older instruction in the pipeline), which is used forinstruction ordering. Conventionally, once unified main mapper 218 hasentered an instruction's logical-to-physical register translation, theinstruction passes to issue queue 222. Issue queue 222 serves as thegatekeeper before the instruction is issued to execution unit 230 forexecution. As a general rule, an instruction cannot leave issue queue222 if it depends upon an older instruction to finish. For this reason,unified main mapper 218 tracks dependency data by storing the issuequeue position data for each instruction that is mapped. Once theinstruction has been executed by general execution engine 224, theinstruction is said to have “finished” and is retired from issue queue222.

Register management unit 214 may receive multiple instructions fromdispatch unit 212 in a single cycle so as to maintain a filled, singleissue pipeline. The dispatching of instructions is limited by the numberof available entries in unified main mapper 218. In some mapper systems,which lack intermediate register mapper 220, if unified main mapper 218has a total of 20 mapper entries, there is a maximum of 20 instructionsthat can be in flight (i.e., not checkpointed) at once. Thus, dispatchunit 212 can conceivably dispatch more instructions than what canactually be retired from unified main mapper 218. The reason for thisbottleneck at the unified main mapper 218 is due to the fact that,conventionally, an instruction's mapper entry could not retire fromunified main mapper 218 until the instruction “completed” (i.e., allolder instructions have “finished” executing).

However, in one embodiment, intermediate register mapper 220 serves as anon-timing-critical register for which a “finished,” but “incomplete”instruction from unified main mapper 218 could retire to (i.e., removedfrom unified main mapper 218) in advance of the instruction's eventualcompletion. Once the instruction “completes,” completion unit 221notifies intermediate register mapper 220 of the completion. The mapperentry in intermediate register mapper 220 can then update thearchitected coherent state of architected register mapper 216 byreplacing the corresponding entry that was presently stored inarchitected register mapper 216.

Further details regarding one embodiment of the mappers and processingassociated therewith are described in U.S. Publication Number2013/0086361, entitled “Scalable Decode-Time Instruction SequenceOptimization of Dependent Instructions, Gschwind et al., published Apr.4, 2013, which is hereby incorporated herein by reference in itsentirety.

As referenced above, processor 200 employs pipelined processing toexecute the instructions fetched from memory. Further details regardingone embodiment of this processing are described with reference to FIG.3, which depicts one example of a processor pipeline. In one example,instructions are fetched into an instruction fetch unit 300, whichincludes, for instance, an instruction fetch (IF) 302, an instructioncache (IC) 304 and a branch predictor 306. Instruction fetch unit 300 iscoupled to a group formation and decode unit 310, which includes one ormore decode stages (Dn) 312, as well as a transfer stage (Xfer) 314 totransfer the decoded instructions to group dispatch (GD) 320. Groupdispatch 320 is coupled to mapping units (MP) 322 (such as architectedregister mapper 216, unified main mapper 218, and/or intermediateregister mapper 220 of FIG. 2), which are coupled to a processing unit330.

Processing unit 330 provides processing for different types ofinstructions. For example, at 331, processing for an instruction thatincludes a branch redirect (BR) 337 is depicted, and includes, forinstance, instruction issue (ISS) 332, register file read (RF) 334,execute (EX) 336, branch redirect 337 to instruction fetch 302, writeback (WB) 346, and transfer (Xfer) 348; at 333, processing for aload/store instruction is depicted that includes, for instance,instruction issue 332, register file read 334, compute address (EA) 338,data cache (DC) 340, format (FMT) 342, write back 346, and transfer 348;at 335, processing for a fixed-point instruction is depicted, andincludes, for instance, instruction issue 332, register file read 334,execute 336, write back 346, and transfer 348; and at 337, processingfor a floating point instruction is depicted that includes, forinstance, instruction issue 332, register file read 334, six cyclefloating point unit (F6) 344, write back 346, and transfer 348.Processing for each type of instruction transfers to group commit (CP)350. The output of group commit 350 is coupled to instruction fetch 302,in the case of interrupts and flushes, as examples.

Further details regarding one embodiment of group formation and decodeunit 310 are described with reference to FIGS. 4A-4C. Referring to FIG.4A, in one embodiment, a plurality of decoders 402, 404, such as Decoder0 and Decoder 1 (e.g., decoders 312 of FIG. 3), respectively, arecoupled to an instruction cache 400 that includes a plurality ofinstructions. In one example, decoder 402 receives a first instruction 0(I0) from instruction cache 400 and decoder 404 receives a secondinstruction 1 (I1) from the cache. Each decoder includes an instructiondecoder 406, 408, respectively, to perform initial decoding of theinstructions and to provide information 410, 412, 414 and 416 about thedecoding. For instance, information 414 and 416 are provided to anoptimization analysis engine (OAE) 418; and information 410 and 412 areprovided to instruction optimizers 422, 420, respectively.

In an embodiment, optimization analysis engine 418 compares the decodedcharacteristics of the instructions in decoders 402 and 404 to determinewhether they correspond to one of a plurality of compound sequences thatare candidates for optimization. Further, optimization analysis engine418 is responsive to a plurality of control signals to suppress therecognition of compound sequences, e.g., when a configuration bit isset. Configuration bits can correspond to implementation specificregisters to disable decode time instruction optimization (DTIO) for allor a subset of compound instructions when a design error has beendetected, when a determination has been made that performing a DTIOsequence is no longer advantageous, when a processor enterssingle-instruction (tracing) mode, and so forth. Optimization analysisengine 418 can be a single entity as shown in FIG. 4A, or can bereplicated, distributed, split or otherwise integrated into one or moreof decoders 402 and 404. The optimization analysis engine can becombined in a single large compound decoder (e.g., including, but notlimited to, a complex decoder comprising optimization analysis engine418, decoder 402 and decoder 404 in a single structure), to facilitatelogic optimization of circuit design improvements.

The optimization analysis engine provides information indicating whethera compound sequence, which can be optimized, has been detected, as wellas information about the nature of the sequence (e.g., which of aplurality of instructions, and/or specific properties of the sequence tobe used by the decoder optimization logic to generate an optimizedsequence). OAE also provides steering logic to a selector to select oneof an unoptimized internal operation (iop) generated by the initialdecode operation, or an iop corresponding to an iop in an optimized DTIOsequence which has been generated by optimization logic under control ofthe OAE control signals, and additional information received fromdecoders having decoded a portion of a compound sequence beingoptimized, such as register specifiers, immediate fields and operationcodes for example.

Optimization analysis engine 418 is coupled to instruction optimizer 420and instruction optimizer 422. Instruction optimizer 420 receivesoperand and instruction information from instruction decoder 408, andinstruction optimizer 422 receives operand and instruction informationfrom instruction decoder 406.

Additionally, instruction optimizer 420 and instruction decoder 406 arecoupled to selection logic 426, and instruction optimizer 422 andinstruction decoder 408 are coupled to selection logic 428. Optimizationanalysis engine 418 may provide selection information 424 to selectionlogic 426, 428 for determining if the respective instructions I0 or I1should generate respective iop instructions (iop(0), iop(1)), or if anoptimized instruction should be used.

Further details of one embodiment of an optimizer 420 (or optimizer 422)is described with reference to FIG. 4B. A first instruction 450 and anext sequential instruction 452 are determined to be candidates foroptimization 454. The first instruction 450 includes an opcode (OP1), asource register field (RA1), an immediate field (I1), and a resulttarget field (RT1). The next sequential instruction 452 includes anopcode (OP2), a source register field (RA2), an immediate field (I2),and a result target field (RT2). If they are not optimizable accordingto a predefined optimization criterion, they are executed in order (OP1456 then OP2 458). If, however, they meet the criterion (including,e.g., that RT1=RA2), the next sequential instruction is modified byoptimizer 420 to include a concatenated value of I1 and I2 to provide anew next sequential instruction 462 that can be executed out-of-orderrelative to the first instruction 460. In one embodiment, the modifiednext sequential instruction has a new effective opcode (OP2x).

Another embodiment of an optimizer 420 (or optimizer 422) is depicted inFIG. 4C. In this example, a first instruction 470 and a next sequentialinstruction 472 are determined to be candidates for optimization 474.The first instruction 470 includes an opcode (OP1), a source registerfield (RA1), another source register field (RB1), and a result targetfield (RT1). The next sequential instruction 472 includes an opcodefield (OP2), a source register field (RA2), another source registerfield (RB2), and a result target field (RT2). If they are notoptimizable according to the predefined optimization criterion, they areexecuted in order (OP1 480 then OP2 482). If, however, they meet thecriterion (including, e.g., that RT1=RA2), the next sequentialinstruction is modified by optimizer 420 to include RB1 to produce a newnext sequential instruction 478 that can be executed out-of-orderrelative to the first instruction 476. In one embodiment, the modifiednext sequential instruction has a new effective opcode (OP2x).

As described herein, one form of optimization is decode time instructionoptimization in which instructions in a group of instructions areoptimized at decode time or pre-decode time (both of which are referredto herein as decode time). A group of instructions includes one or moreinstructions, and in the embodiments described herein, a group includesup to four instructions. However, in other embodiments, a group mayinclude more or less instructions than the examples described herein.

The formation of groups, referred to as group formation or decode groupformation, has limited the ability to optimize instructions when theinstructions span multiple decode groups. For instance, assume that anadd immediate shift (addis) instruction is typically optimized with aload instruction (ld). If, as shown in FIG. 5A, the addis instruction isin Group 1 and the load instruction is in Group 2, the instructions arenot optimized, in this embodiment, since they are in different groups.Thus, even though in one optimization criterion, when an add immediateshift (addis) instruction is followed by a load (ld) instruction,optimization is performed; in this scenario, it is not, since theinstructions are in different decode groups. However, in accordance withone aspect, the groups are reformed to enable the optimization of theaddis instruction from Group 1 with the load instruction from Group 2,as depicted in FIG. 5B.

Further details regarding group formation are described with referenceto FIGS. 6A-6B. Initially, one example of forming groups without takinginto consideration whether the instructions can be optimized (referredto herein as optimization candidacy) is described with reference to FIG.6A. Then, one example of forming groups based on optimization candidacy,in accordance with one or more aspects, is described with reference toFIG. 6B.

Referring to FIG. 6A, in one embodiment, a new empty group is started,STEP 600. Then, a fetched instruction is added to the instruction group,STEP 602, and a determination is made as to whether there are moreinstruction slots in the group, INQUIRY 604. If there are moreinstruction slots in the group (e.g., less than 4 instructions have beenadded thus far), then processing continues with adding an instruction tothe instruction group, STEP 602. However, if there are no moreinstruction slots in the group, then the instruction group is sentthrough the pipeline for further processing, STEP 606. Additionally, adetermination is made as to whether there are more instructions to beprocessed, INQUIRY 608. If there are more instructions, then processingcontinues with STEP 600. Otherwise, group formation is complete.

In the particular embodiment described with reference to FIG. 6A, groupsare formed based on whether there are instruction slots available in thegroups with no regard for the instructions and whether optimization maybe provided. However, with reference to FIG. 6B, one embodiment of groupformation is described in which an instruction group is formed based onwhether instructions may be optimized, such as by decode timeinstruction optimization (DTIO).

Referring to FIG. 6B, in accordance with one aspect, a new emptyinstruction group is started, STEP 650, and a fetched instruction isadded to the instruction group, STEP 652. A determination is then madeas to whether there are more instruction slots in the group, INQUIRY654. If there are more instruction slots in the group, then the next twoor more instructions that have been fetched are analyzed to determinewhether they form an optimization sequence, INQUIRY 656. For instance,predefined optimization criteria are used to determine whether theinstructions may be optimized (e.g., an addis instruction followed by aload instruction). In one example, the optimization is a decode timeinstruction optimization (DTIO), and therefore the optimization sequencemay be referred to herein as a DTIO sequence, or a DTIO candidate or aDTIO candidate sequence (i.e., a candidate for DTIO optimization). Ifthe next instructions do not form an optimization sequence, thenprocessing continues with STEP 652. However, if the next instructionsare a candidate for optimization, then a new group is started and theinstructions of that optimization sequence are added to that new group,STEP 650.

Returning to INQUIRY 654, if there are no more instruction slots in thegroup, then the instruction group is sent through the pipeline forfurther processing, STEP 658. This processing includes, for instance,further decoding, performing optimizations, and/or executing one or moreinstructions associated with the group (e.g., an instruction of thegroup and/or an optimized instruction associated with the group, asexamples). Further, a determination is made as to whether there are moreinstructions to be processed, INQUIRY 660. If there are moreinstructions to be processed, then processing continues with STEP 650.Otherwise, this embodiment of the decode group formation is complete.

In the embodiment described above, the instructions are analyzed todetermine whether the next sequential instructions form an optimizationsequence, such as a DTIO sequence. However, in another embodiment, theanalysis is reduced by simply making a determination as to whether thenext instruction represents the beginning of a possible or potentialoptimization sequence. For instance, if the next instruction is an addisinstruction, then it is assumed that there is an optimization sequencewithout analyzing the instruction(s) after the addis instruction. If thenext instruction represents the beginning of a possible optimizationsequence, then a new group is started. One embodiment of this logic isdescribed with reference to FIG. 6C.

In this embodiment, a new empty group is started, STEP 670, and afetched, instruction is added to the instruction group, STEP 672. Then,a determination is made as to whether there are more instruction slotsavailable in the group, INQUIRY 674. If there are more instruction slotsin the group, then a further determination is made as to whether thenext instruction represents the beginning of a possible optimizationsequence, INQUIRY 676. For instance, is this the type of instructionthat might participate in optimization, such as an addis instruction. Inone example, a data structure may be referenced that lists suchinstructions or parameters for such instructions, and/or predefinedoptimization criteria may be used to make this determination.

If it is determined that the instruction is not the beginning of apossible optimization sequence, then processing continues to STEP 672,in which the instruction is added to the instruction group. However, ifthe next instruction does represent the beginning of a possibleoptimization sequence, then a new group is started, STEP 670.

Returning to INQUIRY 674, if there are no more instruction slots in thegroup, then the instruction group is sent through the pipeline forfurther processing, STEP 678. Additionally, a determination is made asto whether there are more instructions to be processed, INQUIRY 680. Ifthere are more instructions, then processing continues with STEP 670.Otherwise, this embodiment of the decode group formation technique iscomplete.

Although the steps in FIGS. 6A-6C are shown sequentially, one skilled inthe art will recognize that one or more of the steps may be executed inparallel. This is also true for other logic diagrams described herein.

The creation of a new group each time an instruction represents abeginning of an optimization sequence or the beginning of a possibleoptimization sequence may cause poor group formation quality, if it isperformed too aggressively. For instance, assume the last slot in agroup is to include an add immediate shift instruction (addis), and itis decided that when an addis instruction is fetched, a new group is tobe started. Thus, the last slot of the group is empty and a new group isstarted. However, the next instruction is a subtract instruction whichwould not be optimized with the add immediate shift instruction. Now,group 1 has an empty slot, for no reason. Thus, in accordance with oneaspect, the starting of an optimization group is marked in the cache onan I-fetch load. Thus, instead of analyzing the candidate sequence eachtime the instructions are fetched into the processor, a candidateoptimization sequence is identified by storing additional informationinto the instruction cache. Then, when the I-fetch logic fetches aninstruction, it would obtain a marker alongside with the instructionthat indicates, for instance, that such an instruction is considered afirst instruction in an optimization sequence. In one embodiment, theinstruction may be marked as the first instruction in an optimizationsequence, even if this has not been completely determined, but it is apossibility. For instance, if it is decided to only perform partialanalysis before making the indication, but based on this partialanalysis, it is believed the instruction may be the first instruction inan optimization sequence, it is marked as the beginning of anoptimization sequence. The marking reduces processing overhead toanalyze the candidate sequences, and may allow other more exhaustiveanalysis to be performed.

One embodiment of the logic associated with marking the instructions isdescribed with reference to FIG. 7A. Initially, instructions arereceived from the next level of the cache hierarchy or from systemmemory, as examples, STEP 700. A determination is made as to whether theinstruction represents or is considered the start of an optimizationsequence, INQUIRY 702. This may be determined by predefined criteria, adata structure that includes lists of such instructions or parametersdescribing such instructions, or by other means.

If the instruction does not represent the start of an optimizationsequence, then the instruction is marked as such (e.g., not starting aDTIO sequence), STEP 704. The instruction is then placed in the I-cachealong with its marker, STEP 706.

Returning to INQUIRY 702, if the instruction represents the start of anoptimization sequence, then the instruction is marked as starting anoptimization sequence, such as a DTIO sequence, STEP 708. In oneembodiment, an instruction is marked as an optimization or DTIO sequenceif it is to be subject to further analysis during decode. Processingcontinues to STEP 706, in which the instruction is placed in the cachewith its marker. The markers are then used during decode groupformation, as described with reference to FIG. 7B.

Referring to FIG. 7B, in one embodiment, initially, a new empty group isstarted, STEP 730. Then, a fetched instruction is added to theinstruction group, STEP 732. A determination is made as to whether thereare more instruction slots in the group, INQUIRY 734. If there are moreinstruction slots in the group, then a determination is made as towhether the next instruction is marked as the beginning of anoptimization sequence, INQUIRY 736. If not, then processing continues toSTEP 732, in which the instruction is added to the instruction group.Otherwise, processing continues with STEP 730 in which a new empty groupis started.

Returning to INQUIRY 734, if there are no more instruction slots in thegroup, then processing continues with sending the instruction groupthrough the pipeline for further processing, STEP 738. Further, adetermination is made as to whether there are more instructions to beprocessed, INQUIRY 740. If so, then processing continues with STEP 730.Otherwise, processing is complete.

In one embodiment, the start of a new group for each beginning of anoptimization sequence may cause poor group formation. For instance, asshown in FIG. 8A, without the logic of starting a new group at eachinstruction that is considered a start of an optimization sequence, thefirst group includes the add immediate shift instruction, as well as theload instruction; and the second group includes instructions i5 thru i8.However, in accordance with one aspect, if a new group is started foreach optimization sequence, then a new group is started at the addimmediate shift instruction, as shown in FIG. 8B. In this scenario,there are two unused slots in the first group, which was not necessarysince the two instructions of the optimization sequence fit into thefirst group.

Thus, in one embodiment, logic is performed to not necessarily start anew group for the beginning of an optimization sequence, but, instead,only for those that fail to fit into a group. One embodiment of thislogic is described with reference to FIG. 9. As shown, a new empty groupis started, STEP 900, and a fetched instruction is added to theinstruction group, STEP 902. Then, a determination is made as to whetherthere are more instruction slots in the group, INQUIRY 904. If there aremore instruction slots in the group, then a further determination ismade as to whether the next instruction forms an optimization candidate(e.g., based on the markings, analysis, or by other techniques), INQUIRY906. If not, then processing continues with STEP 902 and the instructionis added to the instruction group. However, if the next instructionsform an optimization candidate, then a further determination is made asto whether that candidate sequence will fit in the current group,INQUIRY 908. If it will fit, then processing continues to STEP 902 inwhich the instruction is added to the group. Thus, in this example, theinstructions of the candidate sequence will be placed in the currentgroup. However, if the candidate sequence does not fit in the currentgroup, then processing continues with STEP 900 in which a new group iscreated that will include the optimization sequence.

Returning to INQUIRY 904, if there are no more instruction slots in thegroup, then the instruction group is sent through the pipeline forfurther processing, STEP 910. Further, a determination is made as towhether there are more instructions to be processed, INQUIRY 912. Ifthere are more instructions to be processed, then processing continueswith STEP 900. Otherwise, this aspect of decode logic is complete.

In yet a further embodiment, the possible start of an optimization groupis marked in the cache when instructions are fetched into the cache andannotated with the length of the optimization sequence (e.g., the numberof instructions in the optimization sequence). This information may thenbe used in group formation.

One embodiment of marking an optimization sequence or possibleoptimization sequence is described with reference to FIG. 10A.Initially, instructions are received from the next level of the cachehierarchy or from system memory, as examples, STEP 1000. A determinationis made as to whether the instruction represents the start of anoptimization sequence, INQUIRY 1002. If it does not represent the startof an optimization sequence, then the instruction is so marked, e.g., asnot starting a DTIO sequence, STEP 1004. The instruction is then placedinto the I-cache, along with its marker information, including whetherit is the start of an optimization sequence and the length of thesequence, STEP 1006.

Returning to INQUIRY 1002, if the instruction represents the start of anoptimization sequence, then the instruction is marked as such, e.g., asstarting a DTIO, including the length, STEP 1008, and processingcontinues to STEP 1006, in which the instructions are placed in thecache with the marker (e.g., DTIO and length).

One embodiment of the logic of using the annotated instruction cachethat includes the optimization sequence length is described withreference to FIG. 10B. Initially, an empty group is started, STEP 1030.Then, a fetched instruction is added to the instruction group, STEP1032. A further determination is made as to whether there are moreinstruction slots in the group, INQUIRY 1034. If so, then a furtherdetermination is made as to whether the next instruction is annotated asa start of an optimization sequence, INQUIRY 1036. If the nextinstruction is not so annotated, then processing continues with STEP1032 in which the instruction is added to the instruction group.However, if the next instruction is annotated as a start of anoptimization sequence, then a further determination is made as towhether the candidate sequence of which the instruction is a part willfit entirely into the current group based on the pre-decode information(e.g., the sequence length), INQUIRY 1038. If it will fit into thecurrent group, then processing continues with STEP 1032 in which theinstruction is added to the group. Otherwise, processing continues toSTEP 1030 in which a new group is started that will include thecandidate sequence.

Returning to INQUIRY 1034, if there are no more instruction slots in thegroup, then the instruction group is sent through the pipeline forfurther processing, STEP 1040. Further, a determination is made as towhether there are more instructions to be processed, INQUIRY 1042. Ifthere are more instructions to be processed, then processing continueswith STEP 1030. Otherwise this processing is complete.

As described above, in one embodiment, an optimization candidatesequence is completely contained in a particular decode group. Thedetection and processing of candidate sequences, in one embodiment,follow or use one or more templates. If there are multiple templatesthat can be applied, then the templates are prioritized.

A template is identified by a number of instructions that are to bepresent in the instruction stream. A template may include an input, acondition, and/or an output. The input is a sequence of instructionsthat are to be present. In one embodiment, the instructions to beoptimized by a template are adjacent; i.e., without interveninginstructions; however, in another embodiment, intervening instructionsthat do not reference or interfere with the operands of the templatesequence are included. Instruction opcodes and formats are to matchthose of the specified instructions. There are relationships ofoperands, such that all like-named operands are to match (e.g., ifoperand <R1> occurs in several locations of a template, all associatedoperand fields are to match the same). Variables indicated by literals(i.e., a value directly represented, e.g., as a register number, anumeric value, or other directly specified operand) are to have thevalue indicated by the literal represented directly in the instruction.

Optionally, a template condition that specifies a condition to be metmay be provided. Example conditions include that a constant specified byan instruction is to be a positive, or registers are to be paired, etc.,for a template to be applicable.

The template output specifies an optimized output sequence that includesone or more internal instructions, referred to as internal operations(iops), and operands. They can specify operand fields from the template;functions to generate new fields, values, etc. as appropriate; and/orcan specify values to be retained in conjunction with a continuationsequence number.

Generally, in one embodiment, the optimization of candidate sequencesthat are represented by templates may have a particular syntax. Forinstance, if instruction 1 equals instruction one of a first candidatesequence (i1=cs1.i1) and instruction two equals instruction two of thefirst candidate sequence (i2=cs1.i1) and there are relationships betweena source (src (i2)) and a destination (dst (i1)), then the optimizationsequence is equal to the optimization for the first candidate sequencewith instructions i1 and i2. If this is not true, then internalinstruction 1 is the decode of i1 and internal instruction 2 is thedecode of i2. This is shown, as follows:

If (i1=cs1.i1) and (i2=cs1.i2) and src (i2) = dst (i1) then iop_sequence = perform_cs1_dtio (i1,i2) Else   iop1=decode (i1)  iop2=decode (i2).

One specific template example in which two 16 bit immediate fields arecombined into a single 32 bit immediate field by concatenating andtaking into account the implicit sign extension performed by an addimmediate shift (addis) instruction/add immediate (addi) instruction ondisplacement is as follows:

Template: (destructive (i.e., overwriting) addis/addi sequence)   i1 =addis <r1>, <r2>, <upper>   12 = addi <r1>, <r2>, <lower> =>optimization:   addi32 <r1>, <r2>, combine(<upper>,<lower>)

Templates can be translated to VHDL (Very high speed integrated circuitsHardware Description Language) code, either manually or by a tool. Thecode is to match the instructions of the template(s); matchdependency/operand reuse relationships; and/or generate associatedoutputs.

One example of VHDL code for the above template is:

IF opcode (i1) = OP_ADDIS AND RT(i1) = RT(i2) AND RT(i1) =  RS1(i2) ANDopcode(i2) = ADDI THEN  i1out_op <= IOP_ADDI32;  i1out_rt <= RT(i1); i1out_rs1 <= RS1(i1);  i1out_imm <= combine (si16(i1), si(i2)); i2out_op <= IOP_NOP_ORI;  ELSIF opcode(i1) = ... -- other templates ...  ELSE  i1out_op <= iop(opcode(i1);  ... i2out_op <=iop(opcode(i2));  ... END IF

In at least one embodiment, a candidate sequence with x instructions hasfewer instructions than a decode group with y instructions. Thus, in oneembodiment, VHDL code can be automatically generated from a templatewhere the same candidate sequence is detected and optimized at the firstinstruction, the second instruction, etc. up to the (y−x)th instruction.

In a further template example, more than one instruction may beoutputted by the optimization, as shown below:

Template: (non-destructive addis/addi sequence)   i1 = addis <r1>, <r2>,<upper>   i2 = addi <r3>, <r1>, <lower> => optimization:   addis <r1>,<r2>, <upper>   addi32 <r3>, <r2>, combine(<upper>,<lower>)

This template combines two 16 bit immediate fields into a single 32 bitimmediate field by concatenating and taking into account the implicitsign extension performed by addis/addi on displacement. This formgenerates an intermediate result for r1 because it is not overwritten(not destroyed) by the next instruction in the template. In oneembodiment, templates have parallel semantics, and input logicalregisters are to be renamed without reference to any output renameregisters allocated by rename logic for target registers.

Although in the examples above, two instruction sequences are shown,other sequences may include more than two instructions and still beincluded in the same decode group. One example of an n (e.g., 3)instruction candidate sequence includes, for instance: addpcis+r4, pc,upper; addi r4, r4, lower; and lvx*vr2, r0, r4. This sequence may berepresented in the following template:

i1 = addpcis+ <r1>, <r2>, <upper> i2 = addi <r1>, <r1>, <lower> i3 =lvx* <vrt>, r0, <r1> => optimization:  lvd <vrt>, pc_or_gpr(<r2>),combined (<upper>, <lower>)

The addpcis instruction is to provide program counter (PC) relativeaddressing in a particular architecture, such as the POWER ISA. Theaddpcis instruction is similar to addis, but introduces the value of thePC, rather than the constant 0, when the RA field has a value 0. The pcor gpr function handles expanding the PC special case, since the lvdcase would otherwise handle the RA operand similar to all other RAoperands as a 0 value representing 0, and the other register valuesrepresenting that logical register. Lvd is not an architectedinstruction of, for instance, the POWER architecture, but it is used asan internal operation that describes a load instruction with animplementation defined displacement. In one example, lvx* is aninstruction form that defines the base register (e.g., 4 in thisexample) as having an unspecified value after execution of theinstruction. In one example, the lvx* is new form of the lvx instructionindicating a last use of at least one register (e.g., defined herein tobe the register indicated as <r1> in the template).

One embodiment of a decoder that includes templates to be used indetecting and/or processing instruction sequences, including performingoptimizations, is described with reference to FIG. 11. In this example,instruction decode logic 1100 is coupled to an instruction fetch unit1102 and one or more execution units 1104. The instruction fetch unitincludes instruction fetch logic 1106, which references an instructionaddress register (JAR) 1108. The instruction fetch logic fetchesinstructions from instruction cache I$ 1110 that are forwarded to thedecode unit.

The decode unit includes, for instance, buffers 1114 to accept theinstructions. Buffers 1114 are coupled to a group formation unit 1116.Group formation 1116 is coupled to group decode 1120, which includestemplate detect logic 1122, template optimization 1123 and legacy decodelogic 1126. Template detect logic 1122, template optimization 1123 andlegacy decode 1126 are coupled to a selector 1128. Template detect 1122is further coupled to end of decode group (EODG) storage 1130 thatstores retained information regarding instructions in a decode group. Inone embodiment, the information is for a thread and is associated with athread ID. End of decode group storage 1130 is also coupled to storage1132 that maintains the thread id for multithreaded environments.

Template detect 1122 is used to determine whether there is a templateindicating an optimization for selected instructions, and templateoptimization is used to perform optimizations based on the templates.Selector 128 selects the instructions to be executed (e.g., optimized ornot).

Group formation 116 of instruction decode logic 1100 is used in forminggroups, based on the templates, and/or performing optimizations atdecode time.

Described in detail above are various techniques for forming groups ofinstructions. One or more of the techniques takes into considerationwhether instructions may be optimized if grouped a certain way, as wellas optimizations for the groups themselves (e.g., not needlessly leavingslots empty, etc.).

In the logic diagrams that are described herein that have multiple parts(e.g., FIGS. 7A-7B, 10A-10B, etc.), in a further embodiment, the partsmay be combined into one flow. Additionally, although various steps areshown sequentially, in further embodiments, certain steps may beperformed in parallel. Other variations are also possible.

As will be appreciated by one skilled in the art, one or aspects may beembodied as a system, method or computer program product. Accordingly,one or more aspects may take the form of an entirely hardwareembodiment, an entirely software embodiment (including firmware,resident software, micro-code, etc.) or an embodiment combining softwareand hardware aspects that may all generally be referred to herein as a“circuit,” “module” or “system”. Furthermore, one or more aspects maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, electromagnetic,infrared or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any tangible medium that cancontain or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Referring now to FIG. 12, in one example, a computer program product1200 includes, for instance, one or more non-transitory computerreadable storage media 1202 to store computer readable program codemeans or logic 1204 thereon to provide and facilitate one or moreaspects.

Program code embodied on a computer readable medium may be transmittedusing an appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for one or moreaspects may be written in any combination of one or more programminglanguages, including an object oriented programming language, such asJava, Smalltalk, C++ or the like, and conventional proceduralprogramming languages, such as the “C” programming language, assembleror similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

One or more aspects are described herein with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments. It will beunderstood that each block of the flowchart illustrations and/or blockdiagrams, and combinations of blocks in the flowchart illustrationsand/or block diagrams, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of one or more aspects. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

In addition to the above, one or more aspects may be provided, offered,deployed, managed, serviced, etc. by a service provider who offersmanagement of customer environments. For instance, the service providercan create, maintain, support, etc. computer code and/or a computerinfrastructure that performs one or more aspects for one or morecustomers. In return, the service provider may receive payment from thecustomer under a subscription and/or fee agreement, as examples.Additionally or alternatively, the service provider may receive paymentfrom the sale of advertising content to one or more third parties.

In one aspect, an application may be deployed for performing one or moreaspects. As one example, the deploying of an application comprisesproviding computer infrastructure operable to perform one or moreaspects.

As a further aspect, a computing infrastructure may be deployedcomprising integrating computer readable code into a computing system,in which the code in combination with the computing system is capable ofperforming one or more aspects.

As yet a further aspect, a process for integrating computinginfrastructure comprising integrating computer readable code into acomputer system may be provided. The computer system comprises acomputer readable medium, in which the computer medium comprises one ormore aspects. The code in combination with the computer system iscapable of performing one or more aspects.

Although various embodiments are described above, these are onlyexamples. For example, processing environments of other architecturescan incorporate and use one or more aspects. Additionally, instructiongroups of different sizes may be formed, and/or changes may be made tothe formation techniques. Further, other types of templates may be used.Many variations are possible.

Further, other types of computing environments can benefit from one ormore aspects. As an example, a data processing system suitable forstoring and/or executing program code is usable that includes at leasttwo processors coupled directly or indirectly to memory elements througha system bus. The memory elements include, for instance, local memoryemployed during actual execution of the program code, bulk storage, andcache memory which provide temporary storage of at least some programcode in order to reduce the number of times code must be retrieved frombulk storage during execution.

Input/output or I/O devices (including, but not limited to, keyboards,displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives andother memory media, etc.) can be coupled to the system either directlyor through intervening I/O controllers. Network adapters may also becoupled to the system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems, and Ethernet cards are just a few of the available types ofnetwork adapters.

Referring to FIG. 13, representative components of a Host Computersystem 5000 to implement one or more aspects are portrayed. Therepresentative host computer 5000 comprises one or more CPUs 5001 incommunication with computer memory (i.e., central storage) 5002, as wellas I/O interfaces to storage media devices 5011 and networks 5010 forcommunicating with other computers or SANs and the like. The CPU 5001 iscompliant with an architecture having an architected instruction set andarchitected functionality. The CPU 5001 may have dynamic addresstranslation (DAT) 5003 for transforming program addresses (virtualaddresses) into real addresses of memory. A DAT typically includes atranslation lookaside buffer (TLB) 5007 for caching translations so thatlater accesses to the block of computer memory 5002 do not require thedelay of address translation. Typically, a cache 5009 is employedbetween computer memory 5002 and the processor 5001. The cache 5009 maybe hierarchical having a large cache available to more than one CPU andsmaller, faster (lower level) caches between the large cache and eachCPU. In some implementations, the lower level caches are split toprovide separate low level caches for instruction fetching and dataaccesses. In one embodiment, an instruction is fetched from memory 5002by an instruction fetch unit 5004 via a cache 5009. The instruction isdecoded in an instruction decode unit 5006 and dispatched (with otherinstructions in some embodiments) to instruction execution unit or units5008. Typically several execution units 5008 are employed, for examplean arithmetic execution unit, a floating point execution unit and abranch instruction execution unit. The instruction is executed by theexecution unit, accessing operands from instruction specified registersor memory as needed. If an operand is to be accessed (loaded or stored)from memory 5002, a load/store unit 5005 typically handles the accessunder control of the instruction being executed. Instructions may beexecuted in hardware circuits or in internal microcode (firmware) or bya combination of both.

As noted, a computer system includes information in local (or main)storage, as well as addressing, protection, and reference and changerecording. Some aspects of addressing include the format of addresses,the concept of address spaces, the various types of addresses, and themanner in which one type of address is translated to another type ofaddress. Some of main storage includes permanently assigned storagelocations. Main storage provides the system with directly addressablefast-access storage of data. Both data and programs are to be loadedinto main storage (from input devices) before they can be processed.

Main storage may include one or more smaller, faster-access bufferstorages, sometimes called caches. A cache is typically physicallyassociated with a CPU or an I/O processor. The effects, except onperformance, of the physical construction and use of distinct storagemedia are generally not observable by the program.

Separate caches may be maintained for instructions and for dataoperands. Information within a cache is maintained in contiguous byteson an integral boundary called a cache block or cache line (or line, forshort). A model may provide an EXTRACT CACHE ATTRIBUTE instruction whichreturns the size of a cache line in bytes. A model may also providePREFETCH DATA and PREFETCH DATA RELATIVE LONG instructions which effectsthe prefetching of storage into the data or instruction cache or thereleasing of data from the cache.

Storage is viewed as a long horizontal string of bits. For mostoperations, accesses to storage proceed in a left-to-right sequence. Thestring of bits is subdivided into units of eight bits. An eight-bit unitis called a byte, which is the basic building block of all informationformats. Each byte location in storage is identified by a uniquenonnegative integer, which is the address of that byte location or,simply, the byte address. Adjacent byte locations have consecutiveaddresses, starting with 0 on the left and proceeding in a left-to-rightsequence. Addresses are unsigned binary integers and are 24, 31, or 64bits.

Information is transmitted between storage and a CPU or a channelsubsystem one byte, or a group of bytes, at a time. Unless otherwisespecified, in, for instance, the z/Architecture®, a group of bytes instorage is addressed by the leftmost byte of the group. The number ofbytes in the group is either implied or explicitly specified by theoperation to be performed. When used in a CPU operation, a group ofbytes is called a field. Within each group of bytes, in, for instance,the z/Architecture®, bits are numbered in a left-to-right sequence. Inthe z/Architecture®, the leftmost bits are sometimes referred to as the“high-order” bits and the rightmost bits as the “low-order” bits. Bitnumbers are not storage addresses, however. Only bytes can be addressed.To operate on individual bits of a byte in storage, the entire byte isaccessed. The bits in a byte are numbered 0 through 7, from left toright (in, e.g., the z/Architecture). The bits in an address may benumbered 8-31 or 40-63 for 24-bit addresses, or 1-31 or 33-63 for 31-bitaddresses; they are numbered 0-63 for 64-bit addresses. Within any otherfixed-length format of multiple bytes, the bits making up the format areconsecutively numbered starting from 0. For purposes of error detection,and in preferably for correction, one or more check bits may betransmitted with each byte or with a group of bytes. Such check bits aregenerated automatically by the machine and cannot be directly controlledby the program. Storage capacities are expressed in number of bytes.When the length of a storage-operand field is implied by the operationcode of an instruction, the field is said to have a fixed length, whichcan be one, two, four, eight, or sixteen bytes. Larger fields may beimplied for some instructions. When the length of a storage-operandfield is not implied but is stated explicitly, the field is said to havea variable length. Variable-length operands can vary in length byincrements of one byte (or with some instructions, in multiples of twobytes or other multiples). When information is placed in storage, thecontents of only those byte locations are replaced that are included inthe designated field, even though the width of the physical path tostorage may be greater than the length of the field being stored.

Certain units of information are to be on an integral boundary instorage. A boundary is called integral for a unit of information whenits storage address is a multiple of the length of the unit in bytes.Special names are given to fields of 2, 4, 8, and 16 bytes on anintegral boundary. A halfword is a group of two consecutive bytes on atwo-byte boundary and is the basic building block of instructions. Aword is a group of four consecutive bytes on a four-byte boundary. Adoubleword is a group of eight consecutive bytes on an eight-byteboundary. A quadword is a group of 16 consecutive bytes on a 16-byteboundary. When storage addresses designate halfwords, words,doublewords, and quadwords, the binary representation of the addresscontains one, two, three, or four rightmost zero bits, respectively.Instructions are to be on two-byte integral boundaries. The storageoperands of most instructions do not have boundary-alignmentrequirements.

On devices that implement separate caches for instructions and dataoperands, a significant delay may be experienced if the program storesinto a cache line from which instructions are subsequently fetched,regardless of whether the store alters the instructions that aresubsequently fetched.

In one embodiment, the invention may be practiced by software (sometimesreferred to licensed internal code, firmware, micro-code, milli-code,pico-code and the like, any of which would be consistent with one ormore aspects the present invention). Referring to FIG. 13, softwareprogram code which embodies one or more aspects may be accessed byprocessor 5001 of the host system 5000 from long-term storage mediadevices 5011, such as a CD-ROM drive, tape drive or hard drive. Thesoftware program code may be embodied on any of a variety of known mediafor use with a data processing system, such as a diskette, hard drive,or CD-ROM. The code may be distributed on such media, or may bedistributed to users from computer memory 5002 or storage of onecomputer system over a network 5010 to other computer systems for use byusers of such other systems.

The software program code includes an operating system which controlsthe function and interaction of the various computer components and oneor more application programs. Program code is normally paged fromstorage media device 5011 to the relatively higher-speed computerstorage 5002 where it is available for processing by processor 5001. Thetechniques and methods for embodying software program code in memory, onphysical media, and/or distributing software code via networks are wellknown and will not be further discussed herein. Program code, whencreated and stored on a tangible medium (including but not limited toelectronic memory modules (RAM), flash memory, Compact Discs (CDs),DVDs, Magnetic Tape and the like is often referred to as a “computerprogram product”. The computer program product medium is typicallyreadable by a processing circuit preferably in a computer system forexecution by the processing circuit.

FIG. 14 illustrates a representative workstation or server hardwaresystem in which one or more aspects may be practiced. The system 5020 ofFIG. 14 comprises a representative base computer system 5021, such as apersonal computer, a workstation or a server, including optionalperipheral devices. The base computer system 5021 includes one or moreprocessors 5026 and a bus employed to connect and enable communicationbetween the processor(s) 5026 and the other components of the system5021 in accordance with known techniques. The bus connects the processor5026 to memory 5025 and long-term storage 5027 which can include a harddrive (including any of magnetic media, CD, DVD and Flash Memory forexample) or a tape drive for example. The system 5021 might also includea user interface adapter, which connects the microprocessor 5026 via thebus to one or more interface devices, such as a keyboard 5024, a mouse5023, a printer/scanner 5030 and/or other interface devices, which canbe any user interface device, such as a touch sensitive screen,digitized entry pad, etc. The bus also connects a display device 5022,such as an LCD screen or monitor, to the microprocessor 5026 via adisplay adapter.

The system 5021 may communicate with other computers or networks ofcomputers by way of a network adapter capable of communicating 5028 witha network 5029. Example network adapters are communications channels,token ring, Ethernet or modems. Alternatively, the system 5021 maycommunicate using a wireless interface, such as a CDPD (cellular digitalpacket data) card. The system 5021 may be associated with such othercomputers in a Local Area Network (LAN) or a Wide Area Network (WAN), orthe system 5021 can be a client in a client/server arrangement withanother computer, etc. All of these configurations, as well as theappropriate communications hardware and software, are known in the art.

FIG. 15 illustrates a data processing network 5040 in which one or moreaspects may be practiced. The data processing network 5040 may include aplurality of individual networks, such as a wireless network and a wirednetwork, each of which may include a plurality of individualworkstations 5041, 5042, 5043, 5044. Additionally, as those skilled inthe art will appreciate, one or more LANs may be included, where a LANmay comprise a plurality of intelligent workstations coupled to a hostprocessor.

Still referring to FIG. 15, the networks may also include mainframecomputers or servers, such as a gateway computer (client server 5046) orapplication server (remote server 5048 which may access a datarepository and may also be accessed directly from a workstation 5045). Agateway computer 5046 serves as a point of entry into each individualnetwork. A gateway is needed when connecting one networking protocol toanother. The gateway 5046 may be preferably coupled to another network(the Internet 5047 for example) by means of a communications link. Thegateway 5046 may also be directly coupled to one or more workstations5041, 5042, 5043, 5044 using a communications link. The gateway computermay be implemented utilizing an IBM eServer™ System z® server availablefrom International Business Machines Corporation.

Referring concurrently to FIG. 14 and FIG. 15, software programming codewhich may embody one or more aspects may be accessed by the processor5026 of the system 5020 from long-term storage media 5027, such as aCD-ROM drive or hard drive. The software programming code may beembodied on any of a variety of known media for use with a dataprocessing system, such as a diskette, hard drive, or CD-ROM. The codemay be distributed on such media, or may be distributed to users 5050,5051 from the memory or storage of one computer system over a network toother computer systems for use by users of such other systems.

Alternatively, the programming code may be embodied in the memory 5025,and accessed by the processor 5026 using the processor bus. Suchprogramming code includes an operating system which controls thefunction and interaction of the various computer components and one ormore application programs 5032. Program code is normally paged fromstorage media 5027 to high-speed memory 5025 where it is available forprocessing by the processor 5026. The techniques and methods forembodying software programming code in memory, on physical media, and/ordistributing software code via networks are well known and will not befurther discussed herein. Program code, when created and stored on atangible medium (including but not limited to electronic memory modules(RAM), flash memory, Compact Discs (CDs), DVDs, Magnetic Tape and thelike is often referred to as a “computer program product”. The computerprogram product medium is typically readable by a processing circuitpreferably in a computer system for execution by the processing circuit.

The cache that is most readily available to the processor (normallyfaster and smaller than other caches of the processor) is the lowest (L1or level one) cache and main store (main memory) is the highest levelcache (L3 if there are 3 levels). The lowest level cache is oftendivided into an instruction cache (I-Cache) holding machine instructionsto be executed and a data cache (D-Cache) holding data operands.

Referring to FIG. 16, an exemplary processor embodiment is depicted forprocessor 5026. Typically one or more levels of cache 5053 are employedto buffer memory blocks in order to improve processor performance. Thecache 5053 is a high speed buffer holding cache lines of memory datathat are likely to be used. Typical cache lines are 64, 128 or 256 bytesof memory data. Separate caches are often employed for cachinginstructions than for caching data. Cache coherence (synchronization ofcopies of lines in memory and the caches) is often provided by various“snoop” algorithms well known in the art. Main memory storage 5025 of aprocessor system is often referred to as a cache. In a processor systemhaving 4 levels of cache 5053, main storage 5025 is sometimes referredto as the level 5 (L5) cache since it is typically faster and only holdsa portion of the non-volatile storage (DASD, tape etc) that is availableto a computer system. Main storage 5025 “caches” pages of data paged inand out of the main storage 5025 by the operating system.

A program counter (instruction counter) 5061 keeps track of the addressof the current instruction to be executed. A program counter in az/Architecture® processor is 64 bits and can be truncated to 31 or 24bits to support prior addressing limits. A program counter is typicallyembodied in a PSW (program status word) of a computer such that itpersists during context switching. Thus, a program in progress, having aprogram counter value, may be interrupted by, for example, the operatingsystem (context switch from the program environment to the operatingsystem environment). The PSW of the program maintains the programcounter value while the program is not active, and the program counter(in the PSW) of the operating system is used while the operating systemis executing. Typically, the program counter is incremented by an amountequal to the number of bytes of the current instruction. RISC (ReducedInstruction Set Computing) instructions are typically fixed length whileCISC (Complex Instruction Set Computing) instructions are typicallyvariable length. Instructions of the IBM z/Architecture® are CISCinstructions having a length of 2, 4 or 6 bytes. The Program counter5061 is modified by either a context switch operation or a branch takenoperation of a branch instruction for example. In a context switchoperation, the current program counter value is saved in the programstatus word along with other state information about the program beingexecuted (such as condition codes), and a new program counter value isloaded pointing to an instruction of a new program module to beexecuted. A branch taken operation is performed in order to permit theprogram to make decisions or loop within the program by loading theresult of the branch instruction into the program counter 5061.

Typically an instruction fetch unit 5055 is employed to fetchinstructions on behalf of the processor 5026. The fetch unit eitherfetches “next sequential instructions”, target instructions of branchtaken instructions, or first instructions of a program following acontext switch. Modern Instruction fetch units often employ prefetchtechniques to speculatively prefetch instructions based on thelikelihood that the prefetched instructions might be used. For example,a fetch unit may fetch 16 bytes of instruction that includes the nextsequential instruction and additional bytes of further sequentialinstructions.

The fetched instructions are then executed by the processor 5026. In anembodiment, the fetched instruction(s) are passed to a dispatch unit5056 of the fetch unit. The dispatch unit decodes the instruction(s) andforwards information about the decoded instruction(s) to appropriateunits 5057, 5058, 5060. An execution unit 5057 will typically receiveinformation about decoded arithmetic instructions from the instructionfetch unit 5055 and will perform arithmetic operations on operandsaccording to the opcode of the instruction. Operands are provided to theexecution unit 5057 preferably either from memory 5025, architectedregisters 5059 or from an immediate field of the instruction beingexecuted. Results of the execution, when stored, are stored either inmemory 5025, registers 5059 or in other machine hardware (such ascontrol registers, PSW registers and the like).

A processor 5026 typically has one or more units 5057, 5058, 5060 forexecuting the function of the instruction. Referring to FIG. 17A, anexecution unit 5057 may communicate with architected general registers5059, a decode/dispatch unit 5056, a load store unit 5060, and other5065 processor units by way of interfacing logic 5071. An execution unit5057 may employ several register circuits 5067, 5068, 5069 to holdinformation that the arithmetic logic unit (ALU) 5066 will operate on.The ALU performs arithmetic operations such as add, subtract, multiplyand divide as well as logical function such as and, or and exclusive-or(XOR), rotate and shift. Preferably the ALU supports specializedoperations that are design dependent. Other circuits may provide otherarchitected facilities 5072 including condition codes and recoverysupport logic for example. Typically the result of an ALU operation isheld in an output register circuit 5070 which can forward the result toa variety of other processing functions. There are many arrangements ofprocessor units, the present description is only intended to provide arepresentative understanding of one embodiment.

An ADD instruction for example would be executed in an execution unit5057 having arithmetic and logical functionality while a floating pointinstruction for example would be executed in a floating point executionhaving specialized floating point capability. Preferably, an executionunit operates on operands identified by an instruction by performing anopcode defined function on the operands. For example, an ADD instructionmay be executed by an execution unit 5057 on operands found in tworegisters 5059 identified by register fields of the instruction.

The execution unit 5057 performs the arithmetic addition on two operandsand stores the result in a third operand where the third operand may bea third register or one of the two source registers. The execution unitpreferably utilizes an Arithmetic Logic Unit (ALU) 5066 that is capableof performing a variety of logical functions such as Shift, Rotate, And,Or and XOR as well as a variety of algebraic functions including any ofadd, subtract, multiply, divide. Some ALUs 5066 are designed for scalaroperations and some for floating point. Data may be Big Endian (wherethe least significant byte is at the highest byte address) or LittleEndian (where the least significant byte is at the lowest byte address)depending on architecture. The IBM z/Architecture® is Big Endian. Signedfields may be sign and magnitude, 1's complement or 2's complementdepending on architecture. A 2's complement number is advantageous inthat the ALU does not need to design a subtract capability since eithera negative value or a positive value in 2's complement requires only anaddition within the ALU. Numbers are commonly described in shorthand,where a 12 bit field defines an address of a 4,096 byte block and iscommonly described as a 4 Kbyte (Kilo-byte) block, for example.

Referring to FIG. 17B, branch instruction information for executing abranch instruction is typically sent to a branch unit 5058 which oftenemploys a branch prediction algorithm such as a branch history table5082 to predict the outcome of the branch before other conditionaloperations are complete. The target of the current branch instructionwill be fetched and speculatively executed before the conditionaloperations are complete. When the conditional operations are completedthe speculatively executed branch instructions are either completed ordiscarded based on the conditions of the conditional operation and thespeculated outcome. A typical branch instruction may test conditioncodes and branch to a target address if the condition codes meet thebranch requirement of the branch instruction, a target address may becalculated based on several numbers including ones found in registerfields or an immediate field of the instruction for example. The branchunit 5058 may employ an ALU 5074 having a plurality of input registercircuits 5075, 5076, 5077 and an output register circuit 5080. Thebranch unit 5058 may communicate with general registers 5059, decodedispatch unit 5056 or other circuits 5073, for example.

The execution of a group of instructions can be interrupted for avariety of reasons including a context switch initiated by an operatingsystem, a program exception or error causing a context switch, an I/Ointerruption signal causing a context switch or multi-threading activityof a plurality of programs (in a multi-threaded environment), forexample. Preferably a context switch action saves state informationabout a currently executing program and then loads state informationabout another program being invoked. State information may be saved inhardware registers or in memory for example. State informationpreferably comprises a program counter value pointing to a nextinstruction to be executed, condition codes, memory translationinformation and architected register content. A context switch activitycan be exercised by hardware circuits, application programs, operatingsystem programs or firmware code (microcode, pico-code or licensedinternal code (LIC)) alone or in combination.

A processor accesses operands according to instruction defined methods.The instruction may provide an immediate operand using the value of aportion of the instruction, may provide one or more register fieldsexplicitly pointing to either general purpose registers or specialpurpose registers (floating point registers for example). Theinstruction may utilize implied registers identified by an opcode fieldas operands. The instruction may utilize memory locations for operands.A memory location of an operand may be provided by a register, animmediate field, or a combination of registers and immediate field asexemplified by the z/Architecture® long displacement facility whereinthe instruction defines a base register, an index register and animmediate field (displacement field) that are added together to providethe address of the operand in memory for example. Location hereintypically implies a location in main memory (main storage) unlessotherwise indicated.

Referring to FIG. 17C, a processor accesses storage using a load/storeunit 5060. The load/store unit 5060 may perform a load operation byobtaining the address of the target operand in memory 5053 and loadingthe operand in a register 5059 or another memory 5053 location, or mayperform a store operation by obtaining the address of the target operandin memory 5053 and storing data obtained from a register 5059 or anothermemory 5053 location in the target operand location in memory 5053. Theload/store unit 5060 may be speculative and may access memory in asequence that is out-of-order relative to instruction sequence, howeverthe load/store unit 5060 is to maintain the appearance to programs thatinstructions were executed in order. A load/store unit 5060 maycommunicate with general registers 5059, decode/dispatch unit 5056,cache/memory interface 5053 or other elements 5083 and comprises variousregister circuits, ALUs 5085 and control logic 5090 to calculate storageaddresses and to provide pipeline sequencing to keep operationsin-order. Some operations may be out of order but the load/store unitprovides functionality to make the out of order operations to appear tothe program as having been performed in order, as is well known in theart.

Preferably addresses that an application program “sees” are oftenreferred to as virtual addresses. Virtual addresses are sometimesreferred to as “logical addresses” and “effective addresses”. Thesevirtual addresses are virtual in that they are redirected to physicalmemory location by one of a variety of dynamic address translation (DAT)technologies including, but not limited to, simply prefixing a virtualaddress with an offset value, translating the virtual address via one ormore translation tables, the translation tables preferably comprising atleast a segment table and a page table alone or in combination,preferably, the segment table having an entry pointing to the pagetable. In the z/Architecture®, a hierarchy of translation is providedincluding a region first table, a region second table, a region thirdtable, a segment table and an optional page table. The performance ofthe address translation is often improved by utilizing a translationlookaside buffer (TLB) which comprises entries mapping a virtual addressto an associated physical memory location. The entries are created whenthe DAT translates a virtual address using the translation tables.Subsequent use of the virtual address can then utilize the entry of thefast TLB rather than the slow sequential translation table accesses. TLBcontent may be managed by a variety of replacement algorithms includingLRU (Least Recently used).

In the case where the processor is a processor of a multi-processorsystem, each processor has responsibility to keep shared resources, suchas I/O, caches, TLBs and memory, interlocked for coherency. Typically,“snoop” technologies will be utilized in maintaining cache coherency. Ina snoop environment, each cache line may be marked as being in any oneof a shared state, an exclusive state, a changed state, an invalid stateand the like in order to facilitate sharing.

I/O units 5054 (FIG. 16) provide the processor with means for attachingto peripheral devices including tape, disc, printers, displays, andnetworks for example. I/O units are often presented to the computerprogram by software drivers. In mainframes, such as the System z® fromIBM®, channel adapters and open system adapters are I/O units of themainframe that provide the communications between the operating systemand peripheral devices.

Further, other types of computing environments can benefit from one ormore aspects. As an example, an environment may include an emulator(e.g., software or other emulation mechanisms), in which a particulararchitecture (including, for instance, instruction execution,architected functions, such as address translation, and architectedregisters) or a subset thereof is emulated (e.g., on a native computersystem having a processor and memory). In such an environment, one ormore emulation functions of the emulator can implement one or moreaspects, even though a computer executing the emulator may have adifferent architecture than the capabilities being emulated. As oneexample, in emulation mode, the specific instruction or operation beingemulated is decoded, and an appropriate emulation function is built toimplement the individual instruction or operation.

In an emulation environment, a host computer includes, for instance, amemory to store instructions and data; an instruction fetch unit tofetch instructions from memory and to optionally, provide localbuffering for the fetched instruction; an instruction decode unit toreceive the fetched instructions and to determine the type ofinstructions that have been fetched; and an instruction execution unitto execute the instructions. Execution may include loading data into aregister from memory; storing data back to memory from a register; orperforming some type of arithmetic or logical operation, as determinedby the decode unit. In one example, each unit is implemented insoftware. For instance, the operations being performed by the units areimplemented as one or more subroutines within emulator software.

More particularly, in a mainframe, architected machine instructions areused by programmers, usually today “C” programmers, often by way of acompiler application. These instructions stored in the storage mediummay be executed natively in a z/Architecture® IBM® Server, oralternatively in machines executing other architectures. They can beemulated in the existing and in future IBM mainframe servers and onother machines of IBM® (e.g., Power Systems servers and System x®Servers). They can be executed in machines running Linux on a widevariety of machines using hardware manufactured by IBM®, Intel®, AMD™,and others. Besides execution on that hardware under a z/Architecture®,Linux can be used as well as machines which use emulation by Hercules,UMX, or FSI (Fundamental Software, Inc), where generally execution is inan emulation mode. In emulation mode, emulation software is executed bya native processor to emulate the architecture of an emulated processor.

The native processor typically executes emulation software comprisingeither firmware or a native operating system to perform emulation of theemulated processor. The emulation software is responsible for fetchingand executing instructions of the emulated processor architecture. Theemulation software maintains an emulated program counter to keep trackof instruction boundaries. The emulation software may fetch one or moreemulated machine instructions at a time and convert the one or moreemulated machine instructions to a corresponding group of native machineinstructions for execution by the native processor. These convertedinstructions may be cached such that a faster conversion can beaccomplished. Notwithstanding, the emulation software is to maintain thearchitecture rules of the emulated processor architecture so as toassure operating systems and applications written for the emulatedprocessor operate correctly. Furthermore, the emulation software is toprovide resources identified by the emulated processor architectureincluding, but not limited to, control registers, general purposeregisters, floating point registers, dynamic address translationfunction including segment tables and page tables for example, interruptmechanisms, context switch mechanisms, Time of Day (TOD) clocks andarchitected interfaces to I/O subsystems such that an operating systemor an application program designed to run on the emulated processor, canbe run on the native processor having the emulation software.

A specific instruction being emulated is decoded, and a subroutine iscalled to perform the function of the individual instruction. Anemulation software function emulating a function of an emulatedprocessor is implemented, for example, in a “C” subroutine or driver, orsome other method of providing a driver for the specific hardware aswill be within the skill of those in the art after understanding thedescription of the preferred embodiment. Various software and hardwareemulation patents including, but not limited to U.S. Pat. No. 5,551,013,entitled “Multiprocessor for Hardware Emulation”, by Beausoleil et al.;and U.S. Pat. No. 6,009,261, entitled “Preprocessing of Stored TargetRoutines for Emulating Incompatible Instructions on a Target Processor”,by Scalzi et al; and U.S. Pat. No. 5,574,873, entitled “Decoding GuestInstruction to Directly Access Emulation Routines that Emulate the GuestInstructions”, by Davidian et al; and U.S. Pat. No. 6,308,255, entitled“Symmetrical Multiprocessing Bus and Chipset Used for CoprocessorSupport Allowing Non-Native Code to Run in a System”, by Gorishek et al;and U.S. Pat. No. 6,463,582, entitled “Dynamic Optimizing Object CodeTranslator for Architecture Emulation and Dynamic Optimizing Object CodeTranslation Method”, by Lethin et al; and U.S. Pat. No. 5,790,825,entitled “Method for Emulating Guest Instructions on a Host ComputerThrough Dynamic Recompilation of Host Instructions”, by Eric Traut, eachof which is hereby incorporated herein by reference in its entirety; andmany others, illustrate a variety of known ways to achieve emulation ofan instruction format architected for a different machine for a targetmachine available to those skilled in the art.

In FIG. 18, an example of an emulated host computer system 5092 isprovided that emulates a host computer system 5000′ of a hostarchitecture. In the emulated host computer system 5092, the hostprocessor (CPU) 5091 is an emulated host processor (or virtual hostprocessor) and comprises an emulation processor 5093 having a differentnative instruction set architecture than that of the processor 5091 ofthe host computer 5000′. The emulated host computer system 5092 hasmemory 5094 accessible to the emulation processor 5093. In the exampleembodiment, the memory 5094 is partitioned into a host computer memory5096 portion and an emulation routines 5097 portion. The host computermemory 5096 is available to programs of the emulated host computer 5092according to host computer architecture. The emulation processor 5093executes native instructions of an architected instruction set of anarchitecture other than that of the emulated processor 5091, the nativeinstructions obtained from emulation routines memory 5097, and mayaccess a host instruction for execution from a program in host computermemory 5096 by employing one or more instruction(s) obtained in asequence & access/decode routine which may decode the hostinstruction(s) accessed to determine a native instruction executionroutine for emulating the function of the host instruction accessed.Other facilities that are defined for the host computer system 5000′architecture may be emulated by architected facilities routines,including such facilities as general purpose registers, controlregisters, dynamic address translation and I/O subsystem support andprocessor cache, for example. The emulation routines may also takeadvantage of functions available in the emulation processor 5093 (suchas general registers and dynamic translation of virtual addresses) toimprove performance of the emulation routines. Special hardware andoff-load engines may also be provided to assist the processor 5093 inemulating the function of the host computer 5000′.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of one or more aspects has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A computer program product for facilitatingprocessing in a processing environment, said computer program productcomprising: a computer readable storage medium readable by a processingcircuit and storing instructions for execution by the processing circuitfor performing a method comprising: obtaining an instruction to beexecuted in the processing environment; determining whether theinstruction is to be included in a current group of instructions or anew group of instructions, wherein the determining is based on whetherthe instruction is a candidate for optimization with another instructionaccording to an optimization criterion; based on determining theinstruction is to be included in the new group of instructions, formingthe new group of instructions, the new group of instructions includingthe instruction and the another instruction; and based on forming thenew group of instructions, executing at least one instruction associatedwith the new group of instructions.
 2. The computer program product ofclaim 1, wherein the determining comprises determining whether theinstruction represents a beginning of a potential optimization sequencethat includes the instruction and the another instruction, and whereinthe forming forms the new group of instructions based on the instructionrepresenting the beginning of a potential optimization sequence.
 3. Thecomputer program product of claim 2, wherein the determining whether theinstruction represents the beginning of a potential optimizationsequence comprises checking a marker associated with the instruction,the marker indicating whether the instruction starts a potentialoptimization sequence.
 4. The computer program product of claim 3,wherein the method further comprises marking the instruction with themarker, the marker indicating one of: the instruction is considered asrepresenting the beginning of a potential optimization sequence, or theinstruction is not considered as representing the beginning of apotential optimization sequence, and wherein the marking is performed atinstruction fetch.
 5. The computer program product of claim 1, whereinthe determining whether the instruction is to be included in the currentgroup of instructions or the new group of instructions furthercomprises: checking whether an instruction sequence to be optimized thatincludes at least the instruction and the another instruction fits inthe current group; and forming the new group based on determining theinstruction is a candidate for optimization and the instruction sequencedoes not fit in the current group.
 6. The computer program product ofclaim 5, wherein the checking includes checking a marker associated withthe instruction, the marker indicating a length of the instructionsequence.
 7. The computer program product of claim 6, wherein the methodfurther comprises: determining a number of instructions in theinstruction sequence; and marking the instruction with a marker thatindicates the number of instructions, the marking being performed atinstruction fetch.
 8. The computer program product of claim 1, whereinthe optimization criterion is specified in one or more templates, andwherein at least one template of the one or more templates is to be usedto determine whether the instruction is a candidate for optimization. 9.The computer program product of claim 1, wherein the optimizationcriterion optimizes the instruction and the another instruction bycreating at least one internal operation that represents at least aportion of the instruction and at least a portion of the anotherinstruction.
 10. The computer program product of claim 1, wherein theoptimization is performed at decode time.
 11. A computer system forfacilitating processing in a processing environment, said computersystem comprising: a memory; and a processor in communications with thememory, wherein the computer system is configured to perform a method,said method comprising: obtaining an instruction to be executed in theprocessing environment; determining whether the instruction is to beincluded in a current group of instructions or a new group ofinstructions, wherein the determining is based on whether theinstruction is a candidate for optimization with another instructionaccording to an optimization criterion; based on determining theinstruction is to be included in the new group of instructions, formingthe new group of instructions, the new group of instructions includingthe instruction and the another instruction; and based on forming thenew group of instructions, executing at least one instruction associatedwith the new group of instructions.
 12. The computer system of claim 11,wherein the determining comprises determining whether the instructionrepresents a beginning of a potential optimization sequence thatincludes the instruction and the another instruction, and wherein theforming forms the new group of instructions based on the instructionrepresenting the beginning of a potential optimization sequence.
 13. Thecomputer system of claim 12, wherein the determining whether theinstruction represents the beginning of a potential optimizationsequence comprises checking a marker associated with the instruction,the marker indicating whether the instruction starts a potentialoptimization sequence.
 14. The computer system of claim 11, wherein thedetermining whether the instruction is to be included in the currentgroup of instructions or the new group of instructions furthercomprises: checking whether an instruction sequence to be optimized thatincludes at least the instruction and the another instruction fits inthe current group; and forming the new group based on determining theinstruction is a candidate for optimization and the instruction sequencedoes not fit in the current group.
 15. The computer system of claim 14,wherein the checking includes checking a marker associated with theinstruction, the marker indicating a length of the instruction sequence.16. The computer system of claim 11, wherein the optimization criterionoptimizes the instruction and the another instruction by creating atleast one internal operation that represents at least a portion of theinstruction and at least a portion of the another instruction.
 17. Thecomputer system of claim 11, wherein the optimization is performed atdecode time.
 18. A method of facilitating processing in a processingenvironment, said method comprising: obtaining, by a processor, aninstruction to be executed in the processing environment; determiningwhether the instruction is to be included in a current group ofinstructions or a new group of instructions, wherein the determining isbased on whether the instruction is a candidate for optimization withanother instruction according to an optimization criterion; based ondetermining the instruction is to be included in the new group ofinstructions, forming the new group of instructions, the new group ofinstructions including the instruction and the another instruction; andbased on forming the new group of instructions, executing at least oneinstruction associated with the new group of instructions.
 19. Themethod of claim 18, wherein the determining whether the instruction isto be included in the current group of instructions or the new group ofinstructions further comprises: checking whether an instruction sequenceto be optimized that includes at least the instruction and the anotherinstruction fits in the current group; and forming the new group basedon determining the instruction is a candidate for optimization and theinstruction sequence does not fit in the current group.
 20. The methodof claim 18, wherein the optimization criterion optimizes theinstruction and the another instruction by creating at least oneinternal operation that represents at least a portion of the instructionand at least a portion of the another instruction.